The response of a tensioned flexible sheet immersed in parallel flow

TL;DR

This study investigates how in-plane tension affects the fluid-elastic stability of a flexible sheet in airflow, using wind tunnel experiments and optical tracking to analyze the transition from stability to flutter.

Contribution

It provides new experimental insights into the role of tension-induced rigidity in controlling fluid-elastic instabilities of flexible sheets.

Findings

Tension postpones and suppresses instabilities.

Sheet exhibits nonlinear flutter with higher harmonic components.

Optical tracking reveals detailed 3D displacement evolution.

Abstract

This paper explores the fluid-elastic response of a cantilevered flexible sheet in the presence of uniform airflow. The leading edge of the sheet is clamped, while at the trailing edge, in-plane tension is applied to provide additional rigidity to the sheet's small but finite bending stiffness. We outline a series of experiments performed in a wind tunnel with the purpose of examining fluid-elastic instabilities. In particular, we examine the role of in-plane tension induced rigidity and how it influences static divergence and convected wave instabilities. The flow is characterised by Reynolds numbers of order $10^5$-$10^6$ and we specifically examine a sheet with an aspect ratio of $L/l=1.33$. A unique aspect of this present work, is the direct measurement of the sheet's three-dimensional displacement through an optical tracking method with a grid of passive markers placed on the sheet surface. We show the evolution of the sheet surface from stability, through to divergence, and then finally into flutter. The frequency composition of the flutter event shows higher harmonic components that suggest significant nonlinearities. Tension induced rigidity plays a crucial role in the response of the sheet to the fluid in both postponing and suppressing instabilities.